In various multistage turbomachines used for energy conversion, such as turbines, a fluid is used to produce rotational motion. In a gas turbine engine, for example, air is compressed through successive stages in a compressor and mixed with fuel in a combustor. The combination of air and fuel is then ignited for generating combustion or hot working gases that are directed to turbine stages to produce the rotational motion. The compressor stages and turbine stages typically have stationary or non-rotary components, e.g., vane structures, that cooperate with rotatable components, e.g., rotor blades, for compressing air and expanding the hot working gases.
The rotor blades are typically mounted to disks that are supported for rotation on a rotor shaft. In a known construction for a turbine engine, annular disk arms extend from opposed portions of adjoining disks to define paired annular disk arms. A disk cooling air cavity is formed on an inner side of the paired annular arms between the disks of mutually adjacent stages, and a labyrinth seal may be provided on an inner surface of the stationary vane structures for cooperating with the annular arms to define a gas seal between a path for the hot working gases and the cooling air cavity. The paired annular arms extending from opposed portions of adjoining disks define opposing end faces located in spaced relation to each other forming a gap between the adjoining disks.
Typically, each of the opposing end faces forming this gap may be provided with a slot for receiving a sealing strip, also known as a “belly band” seal, which bridges the gap between the end faces to separate the cooling air flowing through the cooling air cavity from the hot working gases passing through the turbine stages. The sealing strip may be formed of multiple segments, in the circumferential direction, that are interconnected at overlapped or ship-lapped ends, as is described in U.S. Pat. No. 6,315,301, which is incorporated herein by reference.
Inaccessible or confined areas such as, for example, the gap between adjoining disks and the belly band described above, often require routine inspection to verify the integrity of internal engine parts and maintain safe operation of the engine by identifying potential problems, i.e., defects in a part, prior to failure of the part, or to identify the source of an existing problem. For example, problems may be identified through visual inspection by use of a borescope, such as during routine downtime maintenance of the gas turbine engine.
Additional monitoring of the turbine engine may be performed during operation of the engine to further identify the condition of components located within the hot gas path of the engine. While a variety of structures and materials may be incorporated into a borescope used for inspection of the interior turbine components during downtime of the turbine engine when the components are relatively cool, visual monitoring of the turbine components during operation of the turbine provides additional restrictions on the monitoring equipment. Two restrictions that exist for viewing turbine components are 1) line-of-sight configurations where various optical elements are aligned in a straight optical axis puts constraints on the location of any access port and limits the number of turbine components that are even possible to view; and 2) flexible fiber bundles that have been employed to overcome the first restriction are not suitable for the high temperature environment within some portions of a gas turbine nor are they small enough to reach all engine locations.
Accordingly, monitoring of components in turbine engines by continuous monitoring systems has generally been restricted to those locations that present substantially unobstructed access between the outer casing wall and the interior portion of the engine. Thus, there remains the need for devices and techniques to acquire images of high temperature regions of gas turbine engines so that otherwise inaccessible components can be monitored and inspected during operation of the turbine.